1. Field of the Invention
The present invention relates to a system for measuring the position of a tool having a nose or point on a machine tool, which is particularly numerically controlled.
It is necessary to know the gauges of the tool with respect to the gauges of a part to be machined in order to bring about precise machining. In the case of a tool provided with a cutting edge nose, such as a turning or lathe tool, it is necessary to have not only the position of the support of the tool with respect to the support of the part, but also the shape of the tool nose, which varies with wear.
The shape of the tool nose or point is conventionally measured by means of a profile projector, which illuminates it and gives a magnified image thereof on the screen. However, it is necessary to dismantle the tool, which makes it impossible to carry out such a check between two machining passes, particularly for detecting supplementary wear to the tool, because all the gauges of the tool would then be lost.
Moreover, tool gauging is carried out on a separate presetting bench, which consequently makes it necessary to dismantle the tool holder from the machine tool and only permits the reinstallation thereof with an imprecision incompatible with precise machining.
The object of the invention is to overcome these imprecisions by using a system entirely mounted on the machine and involving no dismantling or disassembly of the tool or tool holder.
2. Description of the Related Art
An earlier-dated patent of the Commissariat a l'Energie Atomique (FR-A-2 580 537) makes is possible to gauge a lathe tool without disassembling it and by using an image of said tool on a screen provided with the fixed line of a reticule or graticule serving as the origin. The main settings consist of bringing the tool centre onto a vertical centre height axis ZZ' by adjusting the position of the tool holder on a turret rotating about the centre height axis and placing the turret at a predetermined angular position in order to bring the tool edge tangential to the machining direction XX'. For this purpose use is made of a standard fixed to the chuck of the lathe, whose centre displacement supplies an angular reference. A supplementary setting consists of setting the centre height of the tool with the aid of an image perpendicular to the previous one.
However, this earlier-dated invention requires two separate illuminating and photographing optical systems, which leads to a greater complication of the installation. Moreover, the standard is not integral with the tool and consequently the turret can only carry a single tool. The invention makes it possible to evaluate the coordinates of the centres of a plurality of tools with respect to a single standard rather than correcting the position and orientation of a tool centre with respect to the lathe frame.